Lumber products are typically manufactured in a variety of lengths, ranging from about six feet up to twenty four feet, e.g., conventional dimension lumber is usually manufactured in lengths of 6, 8, 10, 12, 14, 16, 18, 20 and 24 feet, respectively. Following manufacture, this lumber is sorted according to length, width, thickness and grade and then bundled in packages according to the dimensions and grade of the lumber. That is, all boards (lumber) having nominal dimensions of two inches by eight inches by eight feet, for example, and having a pre-determined grade, i.e., grade 1, grade 2 etc., are bundled together in a package (stack) of from about 50 to 300 boards, and these packages are then shipped to various points of use and/or sale. Similar packages are formed of lumber having different dimensions and grade.
Various machinery has been developed in the prior art to automatically sort and stack lumber products. Some prior art machinery is capable of handling lumber in a variety of lengths and some includes independently operable stacker arms. However, all such prior art machinery is relatively complex and expensive in construction and operation. Moreover, conventional lumber stacking machinery sometimes will not operate quickly enough to keep up with other pieces of equipment in a lumber mill.
U.S. Pat. No. 4,290,723 (Johansson), issued 22 Sep. 1981; U.S. Pat. No. 5,613,827 (Vande Linde), issued 25 Mar. 1997; and U.S. Pat. No. 6,655,902 (Dube), issued 2 Dec. 2003, all disclose dual lumber stackers. The complete disclosures of all three of these patents is incorporated herein by reference.
U.S. Pat. No. 7,201,554 (Hogue), issued 10 Apr. 2007, U.S. Pat. No. 7,651,314 (Hogue), issued 26 Jan. 2010, disclose a dual stacker that is complicated.
There is need for lumber stacking machinery that is simple and inexpensive in construction and operation, and which operates at a relatively high speed so that stacking of the lumber to form stacks can proceed at a pace equivalent to the pace of operation of other machinery in the process. Further, such machinery should be capable of continued operation while maintenance or repair is being performed, and should be capable of handling all normal sizes of lumber products without requiring adjustment or modification of the machine.